Many scientists contend that release of halogen refrigerants into the atmosphere deleteriously affects the ozone layer that surrounds and protects the earth from ultraviolet solar radiation. Recent international discussions and treaties, coupled with related regulations and legislation, have renewed interest in devices for recovery and storage of used refrigerants from refrigeration equipment for later purification and reuse or for proper disposal. U.S. Pat. No. 4,261,178, assigned to the assignee hereof, discloses a refrigerant recovery system in which the inlet of a compressor is coupled through an evaporator and through a manual valve to the refrigeration equipment from which refrigerant is to be recovered. The compressor outlet is connected through a condenser to a refrigerant storage container. The condenser and evaporator are combined in a single assembly through which cooling air is circulated by a fan. Content of the storage container is monitored by a scale on which the container is mounted for sensing weight of liquid refrigerant in the container, and by a pressure switch coupled to the fluid conduit between the condenser and the container for sensing vapor pressure within the storage container. A full-container condition sensed at the scale or a high-pressure condition sensed at the pressure switch terminates operation of the compressor motor. A vacuum switch is positioned between the inlet valve and the evaporator for sensing evacuation of refrigerant from the refrigeration system and automatically terminating operation of the compressor motor.
U.S. Pat. Nos. 4,768,347 and 4,809,520, also signed to the assignee hereof, disclose a refrigerant recovery system that includes a compressor having an inlet coupled through an evaporator and through a solenoid valve to the refrigeration equipment from which refrigerant is to be withdrawn, and an outlet coupled through a condenser to a refrigerant storage container or tank. The refrigerant storage container is carried by a scale having a limit switch coupled to control electronics to prevent or terminate further refrigerant recovery when the container is full. The scale comprises a platform pivotally mounted by a hinge pin to a wheeled cart, which also carries the evaporator/condenser unit, compressor, control electronics, and associated valves and hoses.
U.S. Pat. No. 4,805,416, also assigned to the assignee hereof, discloses a number of refrigerant recovery and purification systems in which a refrigerant pump, comprising either the recovery compressor or a separate liquid refrigerant pump, is connected to the storage container for circulating refrigerant from the storage container through a filter/drier for removing water and other contaminants from the refrigerant, and then directing the refrigerant back to the storage container. Operative condition of the filter is indicated by a sight glass positioned in the refrigerant filtration path for indicating concentration of water within the refrigerant, and/or by a differential pressure gauge connected across the refrigerant filter for indicating pressure drop across the filter. The replaceable core of the filter/drier is changed when the differential pressure gauge indicates an excessive pressure differential across the filter/drier unit, or when the sight glass indicates that moisture is not being removed from the refrigerant by the filter/drier.
The sight glass moisture indicator is inexpensive, but does not reliably indicate dry refrigerant for some types of refrigerants. Furthermore, the chemical salts that indicate moisture concentration can be stained or washed off. Even under the best of conditions, conventional sight glass/moisture indicators are not sufficiently sensitive for new refrigerant purity standards on the order of ten parts per million. Moisture content of refrigerant can also be determined through conventional chemical tests, which require sampling of refrigerant and shipment to a laboratory, or on-site testing using a disposable kit or the like. Such chemical test techniques are not well suited, therefore, for use in conjunction with a refrigerant purification system to indicate when the replaceable filter/drier core should be changed.